Field
Exemplary embodiments relates to a wear-resistant copper-base alloy.
Description of Related Art
Conventional copper-base alloys have been obtained through some surface treatment, such as forming an oxide film on the surface of the metal in order to avoid the problem of adhesion. Under frictional wear conditions at a high temperature of over 200° C., for example, a material with a low melting point, in particular, will have adhesive wear generated thereon due to contact between metals with high possibility. However, as the surface treatment performed is typically a thermal treatment step, there have been problems with the increased time and production cost.
In particular, when a copper-base alloy is used as a cladding material for an exhaust valve seat for an ethanol-containing fuel, such as gasoline, the alloy is placed under a reducing atmosphere with strong reduction action of hydrogen. Therefore, formation of an oxide film, which contributes to providing a wear resistant property, is not promoted, and adhesive wear is thus generated due to metal contact. With the progress of such adhesive wear, the wear resistance becomes insufficient. When the wear resistance decreases as described above, there may be cases where wear that is beyond the limit at which the valve seat can function may occur. Specifically, adhesive wear progresses such that a plastic flow is generated in the cladding material upon metal contact with another member (counterpart member), and the cladding material is then worn by the counterpart member, resulting in excessive wear. Therefore, when the matrix of the cladding material is weak, a plastic flow is likely to occur, and adhesive wear is thus likely to occur.
So far, a variety of wear-resistant copper-base alloys have been developed by adjusting the formulation components and the content of each component.
For example, JP H08-225868 A discloses a wear-resistant copper-base alloy containing 1.0 to 10.0% chromium by weight, and JP 4114922 B discloses a wear-resistant copper-base alloy containing 1.0 to 15.0% chromium by weight. However, there have been problems in that when a given amount or more of chromium is added in order to improve the corrosion resistance and the like, the ability to form an oxide film from niobium carbide and molybdenum, or the like would decrease, and sufficient wear resistance cannot thus be obtained. Further, in wear-resistant copper alloys disclosed in JP H04-297536 A and JP H10-96037 A, Nb is added alone, and hard particles form a Laves phase as MoFe silicide or NbFe silicide, thus exhibiting hardness. Therefore, there has been a concern that when a shortage of silicon (Si) in the base occurs, the adhesion resistance may decrease.
As described above, the conventional copper-base alloys have insufficient adhesion resistance and thus have insufficient wear resistance due to the reasons that a plastic flow is likely to occur as the ability to form an oxide film from niobium carbide, molybdenum, or the like is low, and as the matrix is weak.